1. Field of the Invention
The present invention relates to a zoom lens system that is suitable for use in, e.g., an interchangeable-lens digital camera.
2. Description of Related Art
In the related art, zoom lens systems which are suitable for use in photographic cameras and electronic still cameras, etc., have been proposed. For example, Patent Literature Nos. 1 through 4 each disclose a positive-lead five-lens-group zoom lens system configured of a positive lens group, a negative lens group, a positive lens group, a negative lens group and positive lens group, in that order from the object side.
Such a positive-lead zoom lens system can have a reduced overall length at the wide-angle extremity (short focal length extremity) compared to a negative-lead zoom lens system. Furthermore, since a zoom lens system that is configured of five lens groups has an additional freedom with regard to the movement of the lens groups compared to that of a zoom lens system that is configured of four lens groups, aberration fluctuations that occur during zooming can be suppressed.
Whereas, e.g., in a zoom lens system for use in a interchangeable-lens digital camera of recent years, a high optical quality over the entire focal length range (zooming range) has been in demand.
Generally, in a zoom lens system, if the refractive power in a lens group that is used for zooming is increased, a large zoom ratio can be obtained within a predetermined movement amount of such a lens group; however, on the other hand, aberration fluctuations that occur during zooming increase, thereby making it difficult to attain a favorable optical quality over the entire focal length range (zooming range).
The following related art is also known: Japanese Unexamined Patent Publication no. H07-151970, Japanese Unexamined Patent Publication no. 2002-131642, Japanese Unexamined Patent Publication no. 2007-219315, and Japanese Unexamined Patent Publication no. 2009-009121.
The zoom lens systems of the above-mentioned related art also exhibit the problem of not being able to achieve a favorable optical quality over the entire focal Length range (zooming range) due to the refractive power of each lens group (refractive-power balance) being inappropriately set.